Testing a filter's frequency response can be a time-consuming task particularly when a broad range of frequencies are tested in the filter. In known systems, a sine wave generator is connected to a filter under test and generates single tone (i.e. single frequency) test signals. Output signals are captured while test signals at different frequencies are injected into the filter one at a time by the sine wave generator. The frequency response of the filter can be measured after a sufficient number of different frequency signals have been input and the associated output signals captured. When multiple filters must be tested over a broad frequency range, such as in a production-test environment, excessive test time may be required to cycle through multiple test signals at different frequencies for each filter.
In addition to requiring a long test time, the use of individual test frequencies may prevent the accurate characterization of a filter's frequency response. Typically, the frequencies corresponding to points in a filter's response that are 3 dB lower than the pass band are used to measure the filter's bandwidth. Because the actual 3 dB points are not known in production filters, the frequencies selected for the input sine wave are unlikely provide a measurement at the exact 3 dB points. It is likely that the test signals will be input at frequencies that bracket above and below the 3 dB point, which would allow the tester to interpolate the 3 dB point, but would not provide a precise measurement or identification of the 3 dB point. In some filters, such as a notice filter or in a filter with a very narrow pass band, the response in the notch or pass band may be missed by the test equipment if the step size of the input test tones is too big, which would result in an incorrect characterization of the filter's pass band. The existing solutions capture only one frequency at a time and step through a finite set of frequencies to cover the entire band. Many fractional frequencies that appear between the test frequencies cannot be tested. The test times for existing systems are very long and provide only a few data points. As a result, existing test systems provide poor resolution in filter frequency bandwidth testing.